This invention relates to systems for treating leachate, from landfills, for example, to reduce contamination of water supplies.
As described, for example, in the patents to Larson, U.S. Pat. No. 3,586,624, and Brauer, U.S. Pat. No. 3,705,851, the liquid leachate from accumulated waste materials such as landfills may contain undesired constituents that could contaminate underground water supplies as well as surface streams and wells. Many attempts have been made to treat leachate or dispose of it in a way that avoids such contamination of water supplies. The Larson patent, for example, proposes a series of treatment lagoons to receive leachate and subject it to chemical treatment to precipitate suspended solids, as well as stabilizing lagoons and oxidation ponds. Such treatment lagoons, however, occupy a large area and must be isolated from the subsoil to prevent contamination of water supplies. After treatment in the lagoons, the treated leachate is usually returned to the landfill.
The LaVigne U.S. Pat. No. 4,995,969 treats leachate from landfills and the like by applying it to fields containing leachate-tolerant plants, which also requires a large area, and further necessitates control of the pH of the leachate within the tolerance range of the plants.
Attempts have also been made to treat leachate with microorganisms in a digester, as described in the Ghosh U.S. Pat. No. 4,323,367, for example. More complex treatment systems such as disclosed in the Boyd et al. U.S. Pat. No. 5,024,770 in which a clean refuse-derived fuel, produced by pulverizing solid waste containing leachate, is supplied to a furnace which generates heat for drying the solid waste-leachate mixture in a hot air drum.
Other leachate evaporation systems have been proposed which use, for example, plate-type evaporators and centrifugal solid separation units. Such systems have substantial surface areas which can become contaminated and clogged by vaporized leachate residues and require periodic cleaning or replacement. Moreover, they require a number of pumps or rotating centrifuge devices having drive motors which involve further energy expenditure.
Other processes have been used to concentrate waste liquid materials. The Young et al. U.S. Pat. No. 4,016,028, for example, discloses a combination of heating processes, including low-pressure and high-pressure steam heat exchangers and submerged combustion, for concentrating sodium disilicate. Similarly, the Lowe et al. U.S. Pat. No. 3,732,911 shows a submerged combustion evaporator for concentrating spent brine derived from olive processing plants, and the Lilja et al. U.S. Pat. No. 4,278,494 discloses an immersion evaporator for concentrating sulfuric acid solutions, while the Pizzo et al. U.S. Pat. No. 3,622,511 discloses a system for treating raw sewage on a small ship by macerating it and supplying it to an evaporator that employs a submersible burner in which some of the sewage is burned and the solids concentration is increased.
None of the prior art disclosures, however, provides an effective system for concentrating leachate in such a way as to avoid the necessity for evaporator heat exchange surfaces and substantial pumping or centrifuge equipment.